1. Field
This invention relates to an improved distribution network or feed structure for coupling a common feed port to an array of utilization elements, such as radiators, in a frequency-independent cophasal relationship.
2. Prior Art
Waveguide-slot antenna arrays are well known; a comprehensive description of these appears in Chapter 9, pages 9-1 to 9-18 of Antenna Engineering Handbook, edited by Henry Jasik, First Edition, published by McGraw-Hill, Inc., 1961. The structures are mechanically simple and compact, economical to fabricate, and can be designed to provide excellent beam patterns with low sidelobes, and to exhibit only small impedance variations, over substantial bandwidths.
Such arrays exhibit the usually undesirable, and in some cases unacceptable, characteristic that the beam pointing direction varies as a function of frequency. If signals consisting of very short pulses are used, the pulse shape becomes distorted because each fourier component of the pulse is associated with a different pointing direction. In addition, the array aperture must be limited to a size such that the propagation time over the length of the waveguide is substantially less than the pulse duration. Further, waveguide-slot arrays, particularly those in which the slots are inclined, exhibit strong cross-polarized components in certain off-axis directions within the beam, requiring some type of mode filter if they are to be eliminated. Finally, dimensional changes caused by ambient temperature variations can produce undesirable changes in beam pointing.
Other types, for example corporate-fed arrays, can be designed and constructed to provide the desirable performance characteristics of waveguide-slot arrays without the above mentioned undesirable ones. However, such other types are generally much more complex, bulky and expensive to fabricate than waveguide-slot arrays.